The message was seen by Reid’s agent Colin Betteridge. He alerted the police, who are now trying to trace the person who made the threat.

He is known to live in Warrington, Cheshire.

Yesterday a source close to Reid said: “There have been several things on that forum recently, mostly accusing Alex of bringing the sport into disrepute, but this one was a bit different.

Advertisement - article continues below »

“There was a direct threat to kill one of Jordan’s horses and you have to take that kind of thing seriously. Yes we are worried. There are lunatics out there.

“The police went to see Alex at his parent’s home in Aldershot on Friday. He had been training in the morning and then visiting a friend who is in hospital after having a heart attack.

“That’s why he was at his house last night. Normally he’d be at Katie’s. The police talked to him for an hour and he gave a statement.”

The source added: “It’s not other cage-fighters behind this, it’s the people who follow them.

“They get wound up and Alex has been getting an unparalleled amount of grief.”

Jordan is a passionate horsewoman and keeps a stable of six near her Surrey home, including Glamour Girl, s Major Max, Player and Cross Dresser – a horse named after Alex.

Two weeks ago the Sunday Mirror revealed how Jordan had paid for an artist to draw up a coat of arms for herself and lover Alex.

She plans to have it painted on the back of her horse box to show off her love for Alex at the polo and dressage events she regularly competes in across the country.

Meanwhile Jordan was left embarrassed yesterday when a book-signing in Dublin was cut short when just 60 fans turned up to see her.

Jordan smiled for photographers, but looked glum as she signed copies of her book, Standing Out, at one of the country’s busiest shopping centres. After just 20 minutes red-faced Jordan was led out of a back door and driven to the airport.